This invention relates to the technical field of integral hinges joining synthetic resin panels. More particularly, this invention relates to integral hinges having two plies of synthetic resin, namely--a relatively rigid, high durometer, first ply and a relatively flexible, low durometer, second ply, and wherein the first ply has the same hardness and composition as the adjoining synthetic resin panels and the second ply overlies the first ply and is composed of a synthetic resin material having a hardness substantially less than first ply.
It is necessary in many applications for plastic or synthetic resin articles to have inherent flexibility in certain localized areas, without introducing irreversible distortion or fracture of the plastic during flexing. More specifically, many applications require portions of the synthetic resin article to be substantially rigid to provide structural integrity during its intended use. However, for ease of installation certain portions of the article should be relatively flexible, but not so soft as to affect the overall utility of the article for its intended use. Thus, the need arises for synthetic resin articles having a relatively flexible semi-rigid area connecting substantially more rigid areas, approximately analogus to a hinge. Such hinges in synthetic resin articles are used in numerous applications. We enumerate a few illustrative examples to clarify, in a practical sense, the utility of such synthetic resin hinges.
Folding doors are often constructed of numerous rigid plastic panels joined by relatively flexible plastic hinges. The plastic joining material must be sufficiently flexible to permit the individual door panels to fold or collapse to nearly a face-to-face parallel geometry when the folding door is fully open (contracted). Yet the same flexible plastic joining material must be sufficiently durable to withstand many flexing operations, and form an integral part of the door itself when the door is fully closed (extended). Thus, the plastic joining material must have a correct balance flexibility, without being too soft to function as an integral part of the closed door.
A major use for semi-rigid plastics is for construction applications. For example, in open office systems, a semi-rigid plastic is a very convenient way to join space separation panels at a variety of angles for a variety of office configurations, without incurring unacceptable expense in assembly and disassembly.
A further application to construction involves hinges on access panels to enable easy access to office equipment, electrical cabinets, etc. Fexibility is clearly called for as a hinge on an access panel, but certain rigidity and structural integrity is also desirable.
As a final illustrative example, for raceway covers as used in open office systems it is desirable to have rigidity and durability to function as covers, but also a certain flexibility. Rigidity is required of the panels to maintain a structurally sound covering, while some flexibility at the corners is desired for rapid installation in a variety of geometries.
These examples illustrate a few of the cases in which hinge areas in plastic objects are desirable. One common method for constructing such hinges is to coextrude the rigid plastic material in conjunction with a softer, more flexible material, arranging the extrusion geometry such that the softer material is extruded into, and forms a part of the area, where the final product is required to flex. Although such dual-durometer hinges provide a single, integral structure incorporating the hinge, the use of two different durometer plastics makes production to close tolerances difficult. The softer, more flexible material tends to distort relative to the harder material during extrusion and later cooling. Therefore, it is one of the primary purposes of the present invention to produce a dual-durometer integral synthetic resin hinge readily coextruded with a uniform profile.